let arr = ['zg', 'luck'];
arr.push('jam');
// 使用浅拷贝打印出来的值才是当前的数组状态，否则每个打印的结果在浏览器中显示都是一样的
console.log([...arr]); //[ "zg", "luck", "jam" ]
arr.pop();
console.log([...arr]); //[ "zg", "luck" ]
arr.unshift('kobe');
console.log([...arr]); //[ "kobe", "zg", "luck" ]
arr.shift('kobe');
console.log([...arr]); //[ "zg", "luck" ]
